DISEASE CHARACTERISTICS:

• Histologically confirmed adenocarcinoma of the rectum

  • Begins within 15 cm of the anal verge by sigmoidoscopy and/or colonoscopy

• Stage II or III disease

  • Clinical T3 or T4 tumors, as indicated by the following:

    • Tethered or fixed tumor on physical exam
    • cT3, cT4, or N+ disease by endorectal ultrasound or surface coil MRI
• No evidence of metastatic disease by physical examination, chest radiograph, and abdominal/pelvic CT scan
• No primary brain tumor or brain metastases

PATIENT CHARACTERISTICS:

Age

• 18 and over

Performance status

• ECOG 0-2 OR
• Karnofsky 70-100%

Life expectancy

• More than 2 years

Hematopoietic

• WBC at least 3,000/mm^3
• Absolute neutrophil count at least 1,500/mm^3
• Platelet count at least 100,000/mm^3
• No bleeding diathesis or coagulopathy

Hepatic

• Bilirubin normal
• AST/ALT less than 2.5 times upper limit of normal
• INR less than 1.5* NOTE: *For patients receiving warfarin

Renal

• Creatinine normal OR
• Creatinine clearance at least 60 mL/min
• No proteinuria OR
• Protein less than 1 g on 24-hour urine collection

Cardiovascular

• No history of stroke
• No history of deep vein thrombosis

• No clinically significant cardiovascular disease within the past year, including any of the following:

  • Uncontrolled hypertension
  • Myocardial infarction
  • Unstable angina pectoris

• No arterial thromboembolic events within the past 6 months, including any of the following:

  • Transient ischemic attack
  • Cerebrovascular accident
  • Clinically significant peripheral vascular disease
• No history of venous thromboembolic events requiring continuous therapeutic anticoagulation
• No New York Heart Association class II-IV congestive heart failure
• No serious cardiac arrhythmia requiring medication
• No grade II or greater peripheral vascular disease within the past year

Other

• Not pregnant
• Not nursing during and for at least 3-4 months after study participation
• Negative pregnancy test
• Fertile patients must use effective contraception during and for at least 3-4 months after study participation

• No known HIV or HIV risk factors

  • HIV testing not required

• No other concurrent active malignancy except nonmelanoma skin cancer or carcinoma in situ of the cervix

  • Completed therapy and considered to be at less than 30% risk of relapse at least 5 years after all therapy
• No prior allergic reaction attributed to compounds of similar chemical or biological composition to bevacizumab or other study agents
• No serious non-healing wound, ulcer, or bone fracture
• No evidence of CNS disease (e.g., seizures not controlled with standard medical therapy)
• No significant traumatic injury within the past 28 days
• No active infection requiring parenteral antibiotics
• No other concurrent uncontrolled illness
• No concurrent psychiatric illness or social situation that would preclude study compliance

PRIOR CONCURRENT THERAPY:

Biologic therapy

• No prior bevacizumab

Chemotherapy

• No prior fluorouracil-based therapy for any malignancy
• No other concurrent chemotherapy

Endocrine therapy

• No concurrent hormonal therapy except the following:

  • Steroids for adrenal failure or allergic reactions
  • Hormones for non-disease-related conditions (e.g., insulin for diabetes)
  • Intermittent dexamethasone as an antiemetic

Radiotherapy

• No prior pelvic radiotherapy

Surgery

• More than 6 months since prior vascular surgery, stenting, or angioplasty
• More than 28 days since prior major surgery or open biopsy
• More than 7 days since prior biopsy (except rectal cancer)
• More than 7 days since prior placement of vascular access device
• No other concurrent planned major surgery

Other

• More than 10 days since prior full-dose oral or parenteral anticoagulants or thrombolytic agents (except to maintain patency of preexisting, permanent indwelling IV catheters)
• No prior treatment for this malignancy
• No concurrent full-dose oral or parenteral anticoagulants or thrombolytic agents (except to maintain patency of preexisting, permanent indwelling IV catheters)
• No concurrent chronic aspirin use (more than 325 mg/day)
• No concurrent nonsteroidal anti-inflammatory medications (of the kind known to inhibit platelet function at doses used to treat chronic inflammatory diseases)
• No other concurrent investigational agents